Mammography has long been used to screen for breast cancer and other abnormalities. Traditionally, mammograms have been formed on x-ray film. More recently, flat panel digital imagers have been introduced that acquire a mammogram in digital form, and thereby facilitate analysis and storage of the acquired images, and provide other benefits as well. Further, substantial attention and technological development has been dedicated towards obtaining three-dimensional images of the breast, using methods such as breast tomosynthesis. In contrast to the 2D images generated by legacy mammography systems, breast tomosynthesis systems construct a 3D image volume from a series of 2D projection images, each projection image obtained at a different angular displacement of an x-ray source relative to the image detector as the x-ray source is scanned over the detector. The constructed 3D image volume is typically presented as a plurality of slices of image data, the slices being geometrically reconstructed on planes parallel to the imaging detector. The reconstructed tomosynthesis slices reduce or eliminate the problems caused by tissue overlap and structure noise present in single slice, two-dimensional mammography imaging, by permitting a medical professional (e.g., a radiologist) to scroll through the image slices to view underlying structures.
Tomosynthesis systems have recently been developed for breast cancer screening and diagnosis. In particular, Hologic, Inc. (www.hologic.com), has developed a fused, multimode mammography/tomosynthesis system that acquires one or both types of mammogram and tomosynthesis images, either while the breast remains immobilized or in different compressions of the breast. Other companies have proposed the introduction of systems which are dedicated to tomosynthesis imaging; i.e., which do not include the ability to also acquire a mammogram.
However, systems restricted to tomosynthesis acquisition and image display may present an obstacle to acceptance of the tomosynthesis imaging technology, as medical professionals have grown accustomed to screening and analysis of conventional 2D mammogram images. In particular, mammograms provide good visualization of micro-calcifications, and can offer higher spatial resolution when compared with tomosynthesis images. While tomosynthesis images provided by dedicated breast tomosynthesis systems have other desirable characteristics, e.g., better isolation and visualization of structures in the breast, such systems do not leverage the existing interpretation expertise of medical professionals.
Examples of systems and methods that leverage existing medical expertise in order to facilitate the transition to tomosynthesis technology are described in U.S. Pat. No. 7,760,924, which is hereby incorporated by reference in its entirety. In particular, U.S. Pat. No. 7,760,924 describes a method of generating a synthesized 2D image, which may be displayed along with tomosynthesis projection or reconstructed images, in order to assist in screening and diagnosis.